Typical photovoltaic power generating installations comprise a plurality of electrically interconnected photovoltaic (PV) modules. An elemental photovoltaic module is comprised of a laminate that includes a plurality of electrically interconnected photovoltaic (solar) cells that generate a DC power output in response to received solar radiation. Commonly a PV module includes a supporting frame that surrounds the laminate at its periphery. The conventional arrangement comprises connecting all of the PV modules in a given installation to a single inverter which is designed to convert the combined DC power outputs of the modules to an AC power output of selected voltage and frequency.
However, such real-world photovoltaic systems experience performance faults associated with wiring, mounting, orientation, shading, soiling, and snow among others, as well as individual PV module deterioration due to aging, temperature cycling and other factors. Therefore, system diagnosis and monitoring would be of benefit to both the customer and the installer.
Current systems for monitoring and troubleshooting photovoltaic power generating installations require inverters that can monitor and measure inverter temperature and status as well as electrical voltage and current values and also dataloggers that record the information generated by the inverter. Commonly the dataloggers are located inside the building on top of which the photovoltaic power generating system is mounted.
Currently available inverters typically employ a microprocessor-controlled means for measuring DC and AC values and inverter temperature and for communicating that information in digital form to dataloggers or to other devices for storing or displaying data, e.g. RS232, RS485, power line, Ethernet, and wireless communication systems. However, power line communications in residential environments pose a number of complex issues. The primary issue is that the AC power line is inherently a noisy environment. The quality of the signal that is transmitted over power lines is dependent on the number and type of the electrical devices (televisions, computers, hair dryers, etc.) connected to the power lines and switched on at any given time. When appliances in a house turn on or off, they introduce pops and clicks onto the AC utility signal. Energy saving devices often introduce noisy harmonics as well. The system must be designed to manage these common signaling disruptions.
Various types of dataloggers are used with photovoltaic power generating systems. The datalogger may communicate with the inverter by a hard wired connection or wirelessly. The datalogger may be used to record only the inverters' electrical data measurements or it may also be used to record other values such as sunlight and ambient temperature. Various types of display devices also may be used that offer user interaction with the system performance.
Unfortunately current methods of monitoring and diagnosing problems with a PV power generating system comprising a plurality of interconnected PV modules and a single inverter only provide a macro view of the system performance, which includes the inverter, the array and the operating environment as a whole. In a typical monitoring and troubleshooting system, the AC, DC, and environmental measurement components are separated. In other words, the single inverter measures AC and DC values of the combined power output of the interconnected PV modules, but not that of individual PV modules which are physically remote from the inverter. Also the single inverter can measure its own internal temperature but not the temperature of the remote individual modules. Some dataloggers may be adapted for connection to external sensors that record environmental information outside the inverter, usually at a single point, for a whole array of PV modules. Typically such external sensors are mounted at locations determined by the installer and require the installer to run electrical wires from the sensors to the datalogger, so that the value of the sensors is subject to the quality of the installation. Obtaining module level information is too expensive to implement and cumbersome to manage, requiring extensive wiring and additional components such as a temperature sensor for each DC-power generating PV module.
An alternative arrangement comprises connecting each of a plurality of PV modules to its own dedicated inverter, and combining the AC outputs of those inverters for subsequent transmission to a utility grid or a local power load. Each combination of a PV module and its dedicated inverter is identified herein as an AC PV module. A system arrangement comprising a plurality of AC PV modules has many advantages. One such advantage is that each inverter can monitor and measure all input DC and output AC values of an AC PV module as well as inverter temperature, and communicate that measured data to a datalogger or other device that is capable of collecting that data and transferring it to a central database, and/or storing and displaying it locally. However, heretofore there has been lacking a comprehensive method and apparatus for acquiring data from a plurality of AC PV modules that accomplishes detailed self-diagnosis of each module, including measuring, datalogging and communicating data representing AC PV module performance.